A variety of images of the Virgin Mary go by the name Our Lady of Mercy, but in the canonical iconography for this genre the Virgin Mary has a crown, is attended by angels, and shelters a multitude of people under her mantle, which is usually blue.
The image originated with the formation of the Mercedarian Order in the 13th century when Mary was said to appear on the same night to their founder, St. Peter Nolasco; to St. Raymond of Peñafort; and to the king of Aragon. She urged them all to save the many Christians who had been enslaved by Moors and were in danger of succumbing to forced conversion. Peter then established an order dedicated to the Virgin as she had appeared to him, under the name Our Lady of Mercy (Butler, I, 185-6).
The multitude of people beneath the mantle usually appear to be serious middle-class Christians, royals, or nuns and monks. In the closely related Notre Dame de Bon Secours they are angels. In a fresco in Padua they are souls in Purgatory. In one Austrian fresco they are naked souls, so perhaps also supposed to be in Purgatory.
In some German and Austrian examples, Mary may be holding her son in her arms. This type is referred to as the Schutzmantelmadonna:
Prepared in 2016 by Richard Stracke, Emeritus Professor of English, Augusta University. Revised 2018-01-25.